1. Field of the Invention
The present invention relates to a liquid feed pump used in a liquid chromatograph or the like, and more particularly to a diaphragm pump that feeds a liquid by deforming a diaphragm.
2. Description of the Related Art
Various liquid feed pumps have been proposed for use in high performance liquid chromatography. Examples of proposed methods for driving the liquid feed pump include a plunger method (Japanese Patent Application Publication No. 2007-292011), a piezoelectric method in which the diaphragm is driven by a piezoelectric element (Japanese Patent Application Publication No. 2006-118397) or the like. The piezoelectric method of driving the diaphragm is advantaged in that a sliding part such as that employed in the plunger method is absent, and therefore particle generation does not occur, meaning that a liquid feed pump having a long life can be provided. The plunger method, on the other hand, is advantaged in that high pressure discharge can be realized by reducing a surface area of an end part of a plunger (corresponding to a surface area of a cylinder end surface of a pump chamber), and a flow rate can be secured by lengthening a stroke of the plunger.
In recent years it has become necessary in high performance liquid chromatography to perform control very small flow rate at a high-pressure during analysis. On the other hand, large flow rate at a low-pressure is required when introducing and replacing an eluent, cleaning a flow passage or the like. In response to these requirements, a method of feeding a liquid at a high-pressure and very small flow rate as well as at a low-pressure and large flow rate using a splitter (a flow divider) that divides a flow of eluent while employing the plunger method, with which high pressure discharge and the flow rate can be secured, has also been proposed (Japanese Patent Application Publication No. 2003-207494).
The following documents are also pertinent to the related art: Japanese Patent Application Publication No. 2006-29314; Japanese Patent Application Publication No. H6-2663; Japanese Patent Application Publication No. H6-2664; and Japanese Patent Application Publication No. S62-159778.
However, although it is possible with the piezoelectric method to provide a long-life liquid feed pump in which particle generation does not occur, a degree of design flexibility in relation to the stroke (displacement) is small, and it is therefore difficult to apply the piezoelectric method to high performance liquid chromatography in which a liquid must be fed at a high-pressure and very small flow rate as well as at a low-pressure and large flow rate.